Solid core materials which may be encapsulated for use in cleaning products include bleach (both oxygen and chlorine), enzymes, peracid precursors, bleach catalysts and surfactants. A variety of materials and methods have been used to coat such materials with the majority of effort directed to bleach and enzyme encapsulation technology. In particular, bleach particles were coated with fatty acids, polyvinyl alcohol or polyethylene glycols in U.S. Pat. No. 3,908,045 (Alterman et al.). U.S. Pat. Nos. 4,078,099, 4,126,717 and 4,136,052 (Mazzola) teaches coated bleach particles with a mixture of 35-89% by weight fatty acid and 1-16% by weight microcrystalline wax, the wax having melting point of 51.degree.-99.degree. C. Other coating materials used with bleach have included polymer latex, U.S. Pat. No. 4,759,956 (Amer et al.); polycarboxylate materials U.S. Pat. No. 4,762,637 (Aronson et al.); polyethylene waxes of melting point 50.degree.-65.degree. C. EP 132,184 (Scotte); and various waxes, U.S. Pat. No. 4,421,669 (Brichard). The wax coat in Brichard constitutes 0.01-10% of the weight of the bleach to be coated.
Enzymes and bleach were coated with ethylene vinyl acetate, fatty acid, natural waxes, a synthetic resin or an inorganic coating in U.S. Pat. No. 4,421,664 (Ecolab). Other materials used to encapsulate enzymes include silicone oil, petroleum jelly or alcohol waxes, GB 2 186 884 (Albright and Wilson).
Precursors used in cleaning compositions were encapsulated with liquid paraffin waxes and polyvinyl alcohol in U.S. Pat. No. 4,009,113 (Lever).
It was observed that such conventionally coated cores were unstable in aqueous or moist environments and would become inactive prior to use in the cleaning compositions.
In particular, coated bleach particles are unstable in liquid aqueous cleaning compositions because water or other components of the composition which are incompatible with bleach interact with the bleach during storage. The result is little bleach activity remains as a cleaning agent. Similarly, bleach precursors, catalysts, and enzymes are relativity unstable in many liquid aqueous cleaning compositions. Although surfactants are liquid stable they are bleach sensitive and will become unstable in the presence of bleach.
Attempts have been made to increase the stability of encapsulated particles by applying a second coat. Thus Alterman et al. taught optionally applying a second coat of soap to an encapsulated bleach. And U.S. Pat. No. 4,657,784 (Olson) taught double coating a bleach core in an inner coat of paraffin or microcrystalline waxes having melting points of 40.degree.-94.degree. C. and a second coat of material such as sodium carbonate. Encapsulating bleach in an inner coat of fatty acid or waxes and an outer coat of water soluble cellulose ether has also been taught, European Patent Application 307,587 (Olson). Second coats are thought to improve stability of capsules of bleach and other materials, because fissures or gaps in the first coat may allow materials to contact and react with the active core.
These second coats are costly to apply and, while they raise the stability somewhat, do not guarantee that the active material will be available as a cleaning agent after storage.
A variety of methods have been used to encapsulate materials used in cleaning compositions. U.S. Pat. No. 3,847,830 (Williams et al.) describes several methods for enveloping normally unstable peroxygen compounds in water dispersible coatings including paraffin waxes. A coating material is "water dispersible" if, within 30 minutes of adding 2 g of enveloped peroxygen compound to 1 liter of water at 15.degree. C., at least 75% of the peroxygen compound is released. Three of the methods of Williams et al. require the enveloping agent to be molten prior to spraying onto the peroxygen particles in a fluidized bed. Two other methods involve dissolving the enveloping agent in an organic solvent and either spraying the resultant solution onto the particles or immersing them in the bulk solution to achieve coating. Disadvantages of these two methods are the expense of organic solvents and, more importantly, the associated environmental pollution problems.
U.S. Pat. No. 3,856,699 (Miyano et al.) describes a process of dispersing core particles under heating into a waxy material, cooling the resultant dispersion and crushing this into a powder. Thereafter, the powdered waxy material is agitated in an aqueous medium at a temperature higher than the melting point of the waxy material. Waxed core material is then passed into a non-agitated aqueous medium at a temperature lower than the melting point of the waxy material. U.S. Pat. No. 4,919,841 teaches the steps of dispersing active material in melted wax to form an active material/wax dispersion; adding the dispersion to water containing at least one surfactant and emulsifying the active material/wax dispersion for no longer than 4 minutes therein to form capsules; cooling immediately thereafter said capsules and retrieving the cooled capsules form the water to effect capsules of improved quality.
Bleach particles have also been directly sprayed with coating material in fluidized bed apparatuses, as in Brichard. Thus in U.S. Pat. No. 3,908,045 fatty acid coating material was sprayed onto particles. And in U.S. Pat. No. 3,983,254 the spray height of the spray nozzle above the fluidized bed was said to be critical. In U.S. Pat. No. 4,078,099 a rotating drum device was used to apply coating material. Also in U.S. Pat. No. 4,759,956 polymeric latex was sprayed onto core materials (such as bleach) in a fluidized bed operated in a "Wurster" mode.